1. Field of the Invention
The present invention relates to a water separation membrane for separating water from a water solution of ethanol, saccharide or the like.
2. Description of the Related Art
In recent years, from the viewpoint of preventing global warming, it has been called on to reduce emission amount of carbon dioxide which is considered to be one of the reasons of global warming. Therefore, there has been considered to use a mixed fuel of ethanol and a liquid hydrocarbon compound such as gasoline as a vehicle fuel. The ethanol can be yielded from fermentation of a plant material, for example, an agricultural crop such as sugar cane, corn or the like. Since the plant itself, the raw material of the plant material, has absorbed carbon dioxide via photosynthesis, even though the ethanol produced from the plant material is combusted, the emission amount of carbon dioxide is equal to the amount of carbon dioxide absorbed by the plant itself. In other words, the summed emission amount of carbon dioxide can be made theoretically equal to zero, which is the so-called carbon neutral effect. Therefore, the emission amount of carbon dioxide can be reduced in accordance with the amount of ethanol which is used to replace the liquid hydrocarbon compound such as gasoline.
However, if sugar cane, corn and the like are consumed in a large amount as the raw materials of ethanol, there is a problem that the amount thereof supplied as food would be decreased.
In this regard, there has been considered a technology to produce ethanol by using an inedible biomass containing cellulose instead of the plant material, such as sugar cane, corn or the like. As examples of the biomass containing cellulose, wood, rice straw, haulm, bagasse, bamboo, pulp and waste materials originated therefrom, such as waste paper, may be given.
As a production method for ethanol, there has been known a method as disclosed, for example, in Japanese Patent Laid-open No. 2006-88136, in which the biomass containing cellulose is glycosylated by an enzyme to produce a saccharide solution, thereafter, the saccharide solution is fermented into an ethanol water solution by introducing therein ethanol fermentative bacteria.
However, the yielded ethanol water solution according to the mentioned production method is dilute, since the concentration of ethanol is ranged from 0.5 to 5.0 w %. Therefore, it is necessary to condensate it in order to be used as a liquid fuel. Generally, distillation method is adopted to perform the condensation treatment. However, when the concentration of ethanol reaches about 96 w %, ethanol and water are formed into an azeotrope; therefore, it is principally impossible to condensate the ethanol water solution further than 96 w % through the distillation method.
In this regard, there has been known a method as disclosed, for example, in Japanese Patent Laid-open No. H07-185275, in which ethanol is yielded in a concentration of more than 99 w % by separating water from the distillated ethanol water solution according to a pervaporation method. The pervaporation method adopts, for example, a zeolite water separation membrane to separate water from the ethanol water solution at a treatment temperature ranged from 50 to 75° C.
As the condensation treatment for the ethanol water solution, there also has been known a method to yield ethanol in a concentration of more than 99 w % through azeotropic distillation using benzene.
However, according to the condensation treatment for the ethanol water solution, either two steps of distillation and pervaporation are necessary or benzene is needed as an azeotropic compound, therefore, it is disadvantageous.